In a moving coil speaker, a position of a vibration system (including a voice coil and a vibration diaphragm) in a Z-axis direction determines a relative position between the vibration system and a magnetic circuit system, and this relative position affects symmetry between electromechanical coupling factors (BL) and equivalent paraelectric performance (Cms) of the whole system, affecting a vibration state of the system. As a displacement of the vibration system in a low frequency working condition is relatively large, influence of a relative position of the vibration system in the Z-axis under the low frequency on low frequency distortion of the speaker is significant.
At present, due to precision constraints of manufacturing processes and materials, it is hard to reduce the distortion of the speaker in a low frequency condition to be lower than 10%. Or, even if lower distortion of the speaker is realized, it is difficult to guarantee the consistency between products. Therefore, it is necessary to provide a technical scheme that can reduce the low frequency distortion degree of the speaker.